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Diabase (), also called dolerite () or microgabbro, is a
mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks in ...
, holocrystalline, subvolcanic rock equivalent to
volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...
basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
or plutonic
gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ...
. Diabase dikes and
sill Sill may refer to: * Sill (dock), a weir at the low water mark retaining water within a dock * Sill (geology), a subhorizontal sheet intrusion of molten or solidified magma * Sill (geostatistics) * Sill (river), a river in Austria * Sill plate, ...
s are typically shallow intrusive bodies and often exhibit fine-grained to
aphanitic Aphanites (adj. ''aphanitic''; ) are igneous rocks that are so fine-grained that their component mineral crystals are not visible to the naked eye (in contrast to phanerites, in which the crystals are visible to the unaided eye). This ge ...
chilled margins which may contain tachylite (dark mafic glass). ''Diabase'' is the preferred name in North America, while ''dolerite'' is the preferred name in the rest of the English-speaking world, where sometimes the name ''diabase'' refers to altered dolerites and basalts. Some geologists prefer to avoid confusion by using the name ''microgabbro''. The name ''diabase'' comes from the French ', and ultimately from the Greek - meaning "act of crossing over, transition".


Petrography

Diabase normally has a fine but visible texture of
euhedral Euhedral crystals (also known as idiomorphic or automorphic crystals) are those that are well-formed, with sharp, easily recognised faces. The opposite is anhedral (also known as '' xenomorphic'' or ''allotriomorphic''): a rock with an anhedr ...
lath-shaped
plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more p ...
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...
s (62%) set in a finer matrix of clinopyroxene, typically augite (20–29%), with minor
olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...
(3% up to 12% in olivine diabase),
magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With ...
(2%), and ilmenite (2%). Accessory and alteration
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
s include hornblende, biotite, apatite, pyrrhotite, chalcopyrite, serpentine, chlorite, and calcite. The texture is termed ''diabasic'' and is typical of diabases. This diabasic texture is also termed ''interstitial''. The
feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...
is high in anorthite (as opposed to
albite Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula . It is a tectosilicate ...
), the
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
endmember of the plagioclase anorthite-albite solid solution series, most commonly labradorite.


Locations

Diabase is usually found in smaller, relatively shallow intrusive bodies such as
dikes Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes ...
and
sill Sill may refer to: * Sill (dock), a weir at the low water mark retaining water within a dock * Sill (geology), a subhorizontal sheet intrusion of molten or solidified magma * Sill (geostatistics) * Sill (river), a river in Austria * Sill plate, ...
s. Diabase dikes occur in regions of
crustal extension Extensional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the stretching of a planetary body's crust or lithosphere. Deformation styles The types of structure and the geometries formed depend on ...
and often occur in dike swarms of hundreds of individual dikes or sills radiating from a single
volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...
center. The Palisades Sill which makes up the New Jersey Palisades on the
Hudson River The Hudson River is a river that flows from north to south primarily through eastern New York. It originates in the Adirondack Mountains of Upstate New York and flows southward through the Hudson Valley to the New York Harbor between Ne ...
, near
New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
, New York, United States, is an example of a diabase sill. The dike complexes of the British Tertiary Volcanic Province includes Skye, Rum, Mull, and Arran of western
Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to ...
, the
Slieve Gullion Slieve Gullion ( or ''Sliabh Cuilinn'', " Culann's mountain") is a mountain in the south of County Armagh, Northern Ireland. The mountain is the heart of the Ring of Gullion and is the highest point in the county, with an elevation of . At t ...
region of
Ireland Ireland ( ; ga, Éire ; Ulster-Scots: ) is an island in the North Atlantic Ocean, in north-western Europe. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the s ...
, and dolerite dike swarms extending across northern
England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...
towards the Midlands, for example
Rowley Rag Rowley Rag was a volcanic dolerite stone quarried in the stone quarries (known locally as the 'Quacks') of the Rowley Hills in the West Midlands of the United Kingdom, straddling the border of Rowley Regis and Dudley. The main quarry was on Turn ...
. Parts of the Deccan Traps of India, formed at the end of the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
, also include dolerite. It is also abundant in large parts of Curaçao, an island off the coast of
Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...
. Another example of diabase dikes has been recognized in the Mongo area within the Guéra Massif of Chad in Central Africa. In the
Death Valley Death Valley is a desert valley in Eastern California, in the northern Mojave Desert, bordering the Great Basin Desert. During summer, it is the hottest place on Earth. Death Valley's Badwater Basin is the point of lowest elevation in Nort ...
region of California, Precambrian diabase intrusions metamorphosed pre-existing
dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...
into economically important talc deposits. In the Thuringian-Franconian-Vogtland Slate Mountains of central
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...
the diabase is entirely of
Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...
age. They form typical domed landscapes, especially in the
Vogtland Vogtland (; cz, Fojtsko) is a region spanning the German states of Bavaria, Saxony and Thuringia and north-western Bohemia in the Czech Republic. It overlaps with and is largely contained within Euregio Egrensis. The name alludes to the forme ...
. One geotourist attraction is the ''
Steinerne Rose The Steinerne Rose is a rare natural monument. It is a diabase rock formation, that originated on the sea bed from outflowing lava in the middle Devonian, i.e. about 400 million years ago. The lava formed pillow-like bodies which have an interna ...
'' near
Saalburg The Saalburg is a Roman fort located on the main ridge of the Taunus, northwest of Bad Homburg, Hesse, Germany. It is a cohort fort, part of the Limes Germanicus, the Roman linear border fortification of the German provinces. The Saalburg, lo ...
, a natural monument, whose present shape is due to the typical weathering of lava pillows.


Gondwanaland and Australia

A geological event known as the Oenpelli Dolerite intrusive event occurred about 1,720 million years ago in western Arnhem Land, in the Northern Territory, creating curved ridges of Oenpelli Dolerite stretching over . Further west, on the northern coast of Arnhem Land, a "subsurface radial dyke swarm" known as Galiwinku Dolerite, taking its name from the Aboriginal name for Elcho Island, occurs on the Gove Peninsula and continues under the Arafura Sea and on Wessel Islands, including Elcho and Milingimbi Islands. In the Yilgarn Craton of
Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to t ...
, a Proterozoic long dolerite dike, the Norseman-Wiluna greenstone belt is associated with the non-alluvial
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile ...
mining area between
Norseman The Norsemen (or Norse people) were a North Germanic ethnolinguistic group of the Early Middle Ages, during which they spoke the Old Norse language. The language belongs to the North Germanic branch of the Indo-European languages and is the pre ...
and Kalgoorlie, which includes the largest gold mine in Australia, the Super Pit gold mine. West of the Norseman–Wiluna Belt is the Yalgoo-Singleton greenstone belt, where complex dolerite dike swarms obscure the volcaniclastic sediments. Large dolerite sills such as the Golden Mile Dolerite can exhibit coarse-grained texture, and show a large diversity in petrography and geochemistry across the width of the sill. The vast areas of mafic volcanism/ plutonism associated with the
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
breakup of the Gondwana supercontinent in the Southern Hemisphere include many large diabase/dolerite sills and dike swarms. These include the Karoo dolerites of
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...
, the Ferrar Dolerites of
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
, and the largest of these, the most extensive of all dolerite formations worldwide, are found in Tasmania. Here, the volume of
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
which intruded into a thin veneer of
Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...
and
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...
rocks from multiple feeder sites, over a period of perhaps a million years, may have exceeded 40,000 cubic kilometres. In Tasmania, dolerite dominates much of the landscape, particularly alpine areas, with many examples of
columnar jointing Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as joints, result in the formation of a regular array of polygonal prisms, or columns. Columnar jointing occurs in many types of igneo ...
. Early Jurassic activity resulted in the formation of dolerite intrusion in Prospect in
Sydney Sydney ( ) is the capital city of the state of New South Wales, and the most populous city in both Australia and Oceania. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about towards the Blue Mounta ...
, and quarrying of
basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
for roadstone and other building materials has been an important activity there for over 180 years.


Use

Diabase is crushed and used as a construction aggregate for road beds, buildings, railroad beds (rail ballast), and within dams and levees. Diabase can be cut for use as headstones and memorials; the base of the Marine Corps War Memorial is made of black diabase "granite" (a commercial term, not actual granite). Diabase can also be cut for use as ornamental stone for countertops, facing stone on buildings, and paving. A form of dolerite, known as
bluestone Bluestone is a cultural or commercial name for a number of dimension or building stone varieties, including: * basalt in Victoria, Australia, and in New Zealand * dolerites in Tasmania, Australia; and in Britain (including Stonehenge) * felds ...
, is one of the materials used in the construction of
Stonehenge Stonehenge is a prehistoric monument on Salisbury Plain in Wiltshire, England, west of Amesbury. It consists of an outer ring of vertical sarsen standing stones, each around high, wide, and weighing around 25 tons, topped by connec ...
. Diabase also serves as local building stone. In Tasmania, where it is one of the most common rocks found, it is used for building, for landscaping and to erect dry-stone farm walls. In northern County Down, Northern Ireland, "dolerite" is used in buildings such as
Mount Stewart Mount Stewart is a 19th-century house and garden in County Down, Northern Ireland, owned by the National Trust. Situated on the east shore of Strangford Lough, a few miles outside the town of Newtownards and near Greyabbey, it was the Irish s ...
together with Scrabo Sandstone as both are quarried at Scrabo Hill.


See also

* List of rock types


References


External links


Collection of dikes in the Fish River Canyon, Namibia
{{Authority control Aphanitic rocks Ophitic rocks Mafic rocks Subvolcanic rocks